Annular hole cutter

ABSTRACT

A tipped annular hole cutter is made by brazing all the cutting tips (30) simultaneously to the cylindrical wall (12) of the cutter body. The tips (30) have outer and inner lands (32, 34) which locate against the outer and inner surfaces (52, 54) of the cylindrical wall (12). This accurately locates the tips radially during brazing. The radially inner face (46) of the tip (30) is inclined so as to define an inner clearance face which has the necessary circumferential and radial clearances without therebeing any need to grind the inner face (46) after brazing.

This is a divisional of copending application Ser. No. 07/589,719 filedon Sep. 25, 1990.

This invention relates to a method of construction of an annular holecutter.

Annular hole cutters are known having a hollow cylindrical cutter bodywith a plurality of cutting teeth arranged around a lower end thereof,and an upper end thereof adapted for mounting on a rotary driving member(see JP-A-57-211408). The cutting teeth can be of tungsten carbide orhard metal tips brazed to the lower end of a steel body. The body isusually made of heat treated high tensile steel, in order to resist thetorsional forces exerted by the cutting action.

One major or drawback of the above construction is that it is extremelydifficult to grind the radially inwardly facing flanks of the hard tipssince the inner flanks must be inclined both to the tangent at theradius from the inner end of the cutting edge and to the axis of thecutter to provide the necessary clearance angles. Also, it is importantthat the inner end point of the cutting edge on each tip describes thesame annular surface when rotated, otherwise non-uniform loading of thetips ensues. To grind a tip in-situ to this accuracy is extremelydifficult. The abrasive wheels have, of necessity, to be of a smalldiameter and are subject to rapid wear and require frequent dressing.

A further disadvantage of the known construction is the accurateplacement of the tips in the cutter body; locating the tips requirescomplicated placing and clamping means in order to minimise subsequentgrinding operations.

JP-A-57-211408 discloses two projections on each of the tips of anannular hole cutter and these are said to engage the outer periphery ofthe cutter body to locate the tips accurately in a radial direction.However, clamps are needed to hold the tips in place and the innerflanks still require grinding.

It is an aim of the present invention to produce an annular hole cutterin which the accuracy of the positioning of the various cutting edges,clearance angles and rake angles is vastly improved and for which themanufacturing steps are simplified.

It is another object of the invention to manufacture a annular holecutter in which the bits are positively prevented from radially inwardand outward displacement without the use of clamps during brazing.

It is a further object of the invention to form the tips with thedesired circumferential and axial clearances to their inner flanks andto locate the tips accurately during brazing so that the inner flanksrequire no grinding.

In accordance with the invention, in a method of manufacturing a tippedannular hole cutter, the tips have inner and outer lands and are locatedin slots provided in the annular cutter body such that, before the tipsare brazed, the flank of-each tip which faces radially inwardly isaccurately located and is provided with circumferential and axialclearance so that the said flanks do not require subsequent grinding.

The method of construction of the annular hole cutter in accordance withthe invention is described further hereinafter,by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of the blank for a cutter body in which thetip-receiving slots have been cut but before insertion of the tips inaccordance with one embodiment of the present invention;

FIG. 2 is a perspective front view, to a larger scale, of one of thetips for insertion in the slots illustrated in FIG. 1;

FIG. 3 is a perspective rear view of the tip of FIG. 2;

FIG. 4 is a perspective view of the cutter body with some of the tipsinstalled;

FIG. 5 is a fragmentary plan view of the cutter body with the tipsinstalled;

FIG. 6 is a fragmentary-sectional view along the lines VI--VI of FIG. 5,

FIG. 7 is a perspective detail of part of the cutter after brazing andgrinding, and

FIG. 8 is a fragmentary plan view of the cutter with tip brazed andground.

The drawings illustrate the manufacture of a tipped, fluted annular holecutter. A blank 10 (FIG. 1) for the annular cutter body is machined toprovide a hollow cylindrical wall 12 and a drive shank 14. Equallycircumferentially spaced slots 18 are machined into the annular end face16 of the cylindrical wall 12 and are oriented in a skew fashion asshown.

FIGS. 2 and 3 illustrate one of the sintered carbide tips 30 designed tofit in the slots 18. Each tip 30 has two lands 32 and 34 on a first face42 and one land 36 on a second face 48 opposed to the first face. Thelands 32, 34, 36 serve as runners to guide the tip 30 into therespective slot 18 as shown in FIG. 4 so that the first face 42 becomesthe leading face as seen in the intended direction of rotation 20 andthe second face 48 becomes the trailing face.

The first land 32 comprises an elongate rectangular rib or flange whichextends along the edge of the leading face 42 adjacent the flank 44which becomes the radially outer flank in the assembled state. Thesecond land 34 comprises an elongate tapered rib or flange which extendsalong the edge of the leading face 42 adjacent the radially inner flank46. The third land 36 also comprises an elongate tapered rib or flange.It extends along the edge of the trailing face 46 adjacent the radiallyouter flank 44. The outer leading and trailing lands 32 and 36 cooperatewith the outer surface 52 of the cylindrical wall 12 whereas the innerleading land 34 co-ooperates with the inner surface 54 of thecylindrical wall 12. The tips 30 stand proud of the slots 18 whenassembled, as can be seen from FIGS. 4 and 6, when the bottom faces 56of the tips are seated against the bottoms 58 of the slots 18. Thus,there is no need for the lands 32, 34, 36 to extend right up to the topface 60 of the tip 30.

The end face 16 of the cylindrical wall 12 is shallow conical, as can beseen in FIG. 6 and its outer edge 60 may have a slight bevel. FIG. 5shows radii 62 drawn in a radial plane through this outer edge 60. Asalso shown in FIG. 5, these radii lie substantially in the planes of therespective leading side faces 64 (FIG. 1) of the slots 18. This,together with the rectangular shape of the leading outer land 32 ensuresthat the tips 30 are correctly oriented and located before the brazingstep hereinafter described. Because the slots 18 are skewed and becausetheir trailing side faces 66 (FIG. 1) are parallel to the leading sidefaces 64, respectively, the, trailing outer land 36 must be tapered asshown in FIG. 3 to fit snugly against the outer cylindrical surface 52.The inner land 34 fits snugly against the inner cylindrical surface 54.It is tapered because the inner flank 46 is inclined to the cutter axisas will be described later.

Thus, the tips 30 can be placed in position in the slots 18 by hand andcan be retained in these slots, with the cutter body oriented with itsend face 16 uppermost, by a simple hand operation without the need forany clamping and positioning devices. The tips 30 are themsimultaneously brazed in place by placing spelter in the region of eachtip location and by heating the cutter body 10 uniformly about itscircumference. It is sufficient to heat the upper end portion of thecylindrical wall 12 e.g. by induction heating. This is much quicker thanbrazing each tip individually and the circumferential uniformity ofheating ensures a minimum of warping of the cutter body.

After brazing, the annular hole cutter is finished by grinding. Afterthe outer surface 52 of the cutter has been ground down to the correctdiameter, and this includes grinding material off the outer flanks 44 ofthe tips 30, spiral flutes 70 are ground into the outer surface, asshown in FIGS. 7 and 8. Thereafter gullets 72 are ground in the end face16 adjacent the tips 30 so as to communicate with the flutes 70. Finallythe top faces 60 of the tips are ground to form outer and inner endclearance faces 74 and 76 which slope radially outwardly and inwardly,respectively. Flates (not shown) can be ground in the shank 14 forengagement by clamping screws on the spindle of the drilling machine towhich the annular hole cutter is to be fitted.

A cutting edge 78 is formed where the end clearance faces 74, 76 meetthe flute 70 and the gullet 72. However, a finish griding operation canbe performed on the forward face of each tip 30 to produce the desiredfront rake angle.

According to the invention, it is unnecessary to grind the radiallyinner flanks 46 of the tips 30. As can be seen from FIGS. 2 and 3, theradially inner flank 46 is inclined, both with respect to a tangent line80 to the inner periphery of the cutter body at the cutting edge 78 andwith respect to the vertical line 82. Circumferential and axialclearances are thereby imparted to the inner flank 46. Because the tip30 is fitted in a skewed orientation in the cutter body, the tangentline 80 is slightly inclined to the horizontal (with the cutter locatedupright) and is therefore not a true tangent and the vertical line 82 isnot quite parallel to the cutter axis. However the desiredcircumferential and axial clearances at the inner periphery of theannular hole cutter are obtained without grinding the inner faces 46 ofthe tips 30. The accurate radial location of the tips 30 by virtue ofthe outer and inner lands 32, 34, 36 is also essential for avoidance ofgrinding the inner flanks 46, as otherwise the inner end points of thecutting edges 78 would describe circles of differing diameters, leadingto non-uniform tip loading.

Because the tips 30 are made by a sintering process, be they tungstencarbide, hard metal or even ceramic, the powder from which they are mademust be compacted under high pressure in a mould, the tip face 60 cannotbe formed at an angle to provide the desired end clearance angle, thetop face initially slopes in the wrong circumferential direction, as canbe seen by comparing FIGS. 4 and 7. However, it is relatively easy togrind the top faces as they are readily accessible and can be groundusing a relatively large diameter grinding wheel which doesn't requirefrequent dressing. It is possible to design the lands 32, 34, 36 on agiven tip 30 to suit a range of cutter diameters, thereby reducing thenumber of different tips needed to cover a full range of diameters.

The cutters made in accordance with the invention are intended forcutting relatively large diameter holes in hard metals, where ordinarytwist drills would consume too much power, but may also be used forconcrete and masonry.

I claim:
 1. A tipped annular hole cutter comprising a body having acylindrical wall with outer and inner surfaces and a free end surface,and tips secured to said cylindrical wall by metal fusion, the tipsbeing in said wall end surface and defining respective cutting edges,each said tip defining an unground inner clearance face withpredetermined circumferential and axial clearances;each said tip havinglocating means thereon accurately radially locating said tips withinsaid cutter body, the locating means on each said tip including an innerland adjoining said inner clearance face and engaging said inner surfaceof said body.
 2. An annular hole cutter according to claim 1, whereinsaid cylindrical wall has tip-receiving slots therein which extend witha preselected orientation from said free end surface of said wall, saidcutter body having an intended direction of rotation about an axis ofrotation, and wherein each said tip includes a leading face, a trailingface, an inner face, an outer face, a tip surface and a bottom face,said inner face having a preselected inclination, and said tips arereceived in said slots so that said leading faces of said tips face insaid intended direction of rotation, said preselected inclination ofsaid tip inner face being so chosen in relation to the preselectedorientation of said slots that the tip inner face defines said ungroundinner clearance face.
 3. An annular hole cutter according to claim 2,wherein said preselected inclination is so chosen that said ungroundinner clearance face has both circumferential and axial clearance.
 4. Anannular hole cutter according to claim 1, further comprising spiralflutes in an outer surface of said cylindrical wall and gullets in saidwall end surface.
 5. A tipped annular hole cutter comprising a bodyhaving a cylindrical wall with outer and inner surfaces and a free endsurface, and tips secured to said cylindrical wall by metal fusion, thetips being in said wall end surface and defining respective cuttingedges, each said tip defining an unground inner clearance face withpredetermined circumferential and axial clearances;said tips includelocating means for accurately locating said tips within said cutterbody, said locating means including three lands, a first land extendingpartially along a peripheral edge of a first surface of said tip, asecond land extending along the peripheral edge of the first surfaceopposite said first land and a third land extending along the edge of asecond surface, opposite the first surface of the tip such that thethird land is opposite the first land.
 6. An annular hole cutteraccording to claim 5, wherein said first and third lands cooperate withthe outer surface of said cylindrical wall and said second landcooperates with the inner surface of said cylindrical wall.
 7. Anannular hole cutter according to claim 5, wherein said first land issubstantially rectangular, and said second and third lands are taperedto fit snugly against the inner and outer cylindrical surfacesrespectively.
 8. An annular hole cutter according to claim 5, whereinsaid second and third lands each have a base adjacent said bottom faceof said tip and a top, said second land having a smaller base taperingto larger top and said third land having a larger base tapering to asmaller top.
 9. An annular hole cutter according to claim 5, whereinsaid lands extend partially along the edge of each respective surface.10. An annular hole cutter according to claim 5, wherein said first andsecond lands are on the leading surface of said tip and said third landis on the trailing surface of said tip.
 11. An annular hole cutteraccording to claim 7, wherein said tip-receiving slots have leading sidefaces which lie in radial planes, said leading side faces cooperatingwith said substantially rectangular first land to ensure properorientation of said tips.